Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

Suggested Citation:"Status Report on the Alteration of Fatty Acid and Sterol Composition in Lipids in Meat, Milk, and Eggs." National Research Council. 1976. Fat Content and Composition of Animal Products: Proceedings of a Symposium. Washington, DC: The National Academies Press. doi: 10.17226/22.

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JOEL BITMAN
Status Report on the
Alteration of Fatly Acid and
Stero! Composition in Lipids
in Meat, Milk' and Eggs
Demonstration of the high positive correlation between saturated fat
intake and heart disease (Figure 1) and between blood cholesterol
levels and heart disease (Figure 2) has made the American consumer
wary of the fat in meat, milk, and eggs. The percentage of fat con-
tributed by these food groups over a 20-year period is shown in Table 1
(Economic Research Service, 1965; Agricultural Statistics, 1969~. A
50% decline in butter consumption and 20% decline in egg consump-
tion were especially meaningful trends. The American consumer has
maintained a high consumption of beef, but that portion that is fat
is an unwanted obesity-inducing nutrient. Thus, in 1973 approximately
2.5 billion pounds of excess fat, valued at 1.15 billion dollars, were
trimmed from beef carcasses (Hendricks, 19741. The animal scientist,
reluctantly and belatedly, has finally recognized and accepted this
message from the marketplace.
Within the last few years, research has been directed towards altering
animal fats to make them more acceptable to the consumer, i.e., to in-
crease the polyunsaturated fats in meat and milk and to lower the
cholesterol in eggs. The task that faces the scientist who wants to change
the lipid composition of the ruminant is considerably more difficult than
it is to change the body fat composition of the nonruminant. In mono-
gastric animals, such as man, pig, and chicken, body fat can be changed
readily by changing the composition of the diet. Many experiments
200

Alteration of Fatty Acid and Sterol Composition in Lipids 201
40
20
20
10
_ CHD DEATH RATE
PER 1000
n n n n
~ CALORIES FROM SATURATED FATS
~n 11
GR JAP NETH FIN
YUGO IT US
FIGURE 1 Coronary heart disease deaths
and percentage of total calories provided by
saturated fats in the diet of men from seven
countries (Keys, 1970).
have demonstrated that if higher levels of dietary polyunsaturated fats
are fed to pigs and chickens, these polyunsaturated dietary lipids will
be absorbed and incorporated into body fat. In ruminants, however, if
increased amounts of polyunsaturated fats are fed, they are utilized
by microorganisms in the rumen or metabolized by these organisms to
form saturated and mono-unsaturated fatty acids; as a result, the meat
and milk fat do not show any increase in polyunsaturated fat. The data
in Table 2 demonstrate that although the normal plant diet of the
ruminant is primarily polyunsaturated, both meat and milk fat normally
TABLE 1 Contribution of Fat from Various Food Groups a
Percentage of Fat
Contributed by 1947-19491968 Change (% )
-
Meat, including fish 33.5%35.2% +S
Milk and dairy products,
including butter 21.6%17.1% -20
Eggs 4.3 %3.4% -20
Total 59.4%55.7% -6
a Data from ERS, 1965; and Agricultural Statistics, 1969.

Alteration of Fatty Acid and Sterol Composition in Lipids 203
ruminant meat and milk. T. W. Scott and his colleagues in Australia
(Scott et al., 1970) coated polyunsaturated oils with a protein and then
protected these particles from microbial attack in the rumen by treat-
ment with formaldehyde. The coated oils passed through the rumen
(pH 6-7) and into the abomasum and omasum (ply 2-3), where the
more acid conditions hydrolyzed the protein-formaldehyde coat, re-
leasing the intact dietary polyunsaturated oil, which could then be ab-
sorbed and incorporated into body and milk lipid. The process had
earlier been utilized by Ferguson et al. (1967) to increase wool growth
of sheep by protecting dietary casein from microbial degradation in the
rumen. This innovative technique has been the subject of intensive
research within the last 4 years and has, for the first time, provided a
range of new polyunsaturated ruminant foods.
An attempt has been made in this review to summarize research di-
rected towards altering the fatty-acid and sterol composition of meat,
milk, and eggs. The typical fatty-acid composition of the foods of animal
origin is shown in Table 3. This is the base upon which the experimental
alterations have been made. It can be seen that ruminant fat contains
more saturated fatty acids and less polyunsaturated fatty acids than do
swine and poultry fat. Of the three major dietary components fats, pro-
teins, and carbohydrates most attention has been given to the effects of
feeding fats upon the fatty-acid and cholesterol composition of the
animal. The tables are intended to group typical experimental findings
and are not necessarily comprehensive and complete.
TABLE 3 Typical Fatty-Acid Composition (Weight Percent) of Fat
from Different Animal Sources a
Ruminant Nonruminant
Fatty Acid Milk Beef Pork Poultry Eggs
Saturated
Lower C`-C1. 11
Myristic 14:0 12 3 1 1 1
Palmitic 16:0 31 26 25 25 23
Stearic 18:0 11 14 14 4 4
Unsaturated
Palmitoleic 16:1 4 3 3 7 5
Oleic 18:1 24 47 47 43 47
Linoleic 18:2 3 3 8 18 16
Linolenic 18 :3 1 1 - 2
Others 3 3 2 2 2
a Data from Hilditch and Williams ( 1964) and Bitman et al. (1974a).

204
A SYNOPSIS OF ALTERATIONS IN THE
LIPID COMPOSITION OF SWINE
JOEL BITMAN
A summary of the changes brought about in fatty-acid composition by
experimental dietary alterations in swine is presented in Table 4. The
data clearly demonstrate the ready capacity of the pig to store fat of
the type present in its diet. A wide variety of plant and fish oils, con-
taining large quantities of polyunsaturated fatty acids, were fed to pigs;
and the polyunsaturated fats were promptly absorbed and incorporated
into their body fat. Most of these studies were conducted with growing
pigs (8-28 weeks); end the depot fat alterations, although rapid, re-
quired several months to achieve equilibrium. Experiments during the
twenties and thirties, in which polyunsaturated fats were added to the
diet, produced a soft or oily pork, characterized by a high linoleic ( 18: 2)
and a low palm~tic ( 16: 0) and low stearic ( 18: 0) content.* Consumer
acceptability was poor.
While Table 4 may appear to indicate that alterations in the fatty-acid
composition of swine have been well explored, I would suggest that this
table, based upon approximately twenty reports, instead shows that fat
~ The first number refers to the length of the carbon chain in the fatty acid; the
second, to the number of double bonds in the chain.
TABLE 4 Fatty Acid Changes in Pig Fat a
Diet 18:2 18:1 18:0 16:0 16:1 20-22 References
Plant Lipids
Corn, corn oil
+
67, 68, 69, 71, 82,
123
Soybeans,
soybean oil + - - - 16, 68, 69
Peanuts + - - - 68, 69
Cottonseed oil + - + - 70
Fish Lipids
Menhaden oil
Whale oil
Cod liver oil-lard
Animal Lipids
Tallow
Cholesterol
VFA
High carbohydrate
Vitamin D
Copper
17, 18
83
+ + 84
O O O O
+
+ +
O + - O
123
113
14
66
113
2, 30, 142, 212
a CODE: ~ = increase,-= decrease, and 0 = no change.

Alteration of Fatty Acid and Sterol Composition in Lipids 205
modification research in pigs is relatively limited when compared to the
number of studies on the role of fat in cardiovascular disease, where
literature references run into the hundreds. The advent of modern
gas-liquid chromatography has made investigation in this area much
more practicable. Thus, the mechanism for control of fat composition in
swine would seem to be susceptible to more exact elucidation. There are
some additional, scattered literature references that indicate that several
other factors affect fatty-acid composition (sex, age, breed, starvation,
temperature), but this limited information was not included.
A SYNOPSIS OF ALTERATIONS IN THE LIPID COMPOSITION
OF POULTRY DEPOT AND EGG LIPIDS
Summaries of the changes that can be effected in fatty-acid composition
of poultry depot fat and egg lipids are presented in Tables 5 and 6.
Several major features are apparent:
1. Alterations in egg lipids are complete within 16 days, while
depot fat changes are much slower, requiring several months to reach
an equilibrium. This difference reflects ovum maturation time in the
egg-laying cycle and a relatively rapid transfer of blood lipids to a small
fat compartment (egg lipids) in contrast to a much slower balance
between blood lipids and a large lipid compartment (depot fat).
2. The chicken stores fat of the type present in its diet: dietary
saturated or unsaturated fat causes the deposition of lipids of that re-
spective type in the depot fat.
3. Dietary unsaturated fats pass readily into egg lipids, thus ingestion
of a wide variety of unsaturated plant oils results in the appearance
of the characteristic unsaturated fatty acids in the egg. Dietary saturated
fats, however, have relatively little influence upon the composition of
egg lipids.
4. An approximate inverse relationship exists between linoleic acid
and oleic acids in egg and tissue lipids in response to dietary unsaturated
fat ingestion. Particularly because of the marked resistance to change
of the saturated fatty acids in egg lipids, most compositional changes in
response to dietary fats occur in the relative proportions of 18:2 and
18:1.
To the extent that generalizations between species are valid in these
two monogastric animals, the chicken and the pig, it is apparent that
the body fat of swine and poultry will reflect either greater saturation or
unsaturation, depending upon the composition of the diet. Egg lipid
composition, however, can be altered readily only in the direction of
more unsaturated lipids.

208
SYNOPSIS OF ALTERATIONS IN EGG CHOLESTEROL
CONTENT
JOEL BITMAN
Table 7 presents a summary of factors that can alter egg cholesterol
content. Such limited studies as have been carried out on age and season
as factors influencing egg cholesterol have not been included. A large
number of studies dealing with changes in serum cholesterol and liver
cholesterol in poultry, but which do not contain data on egg cholesterol,
are not discussed in this review.
Cholesterol, like the other lipids in eggs, can be altered by dietary
means. Studies with labeled acetate (Kritchevsky and Kirk, 1951,
Kritchevsky et al., 1951), cholesterol (Andrews et al., 1965, 1968;
Connor e! al., 1965), and triglycerides (Budowski et al., 1961) and the
experiments with cholesterol inhibitors in which desmosterol builds up
in the egg (Burgess et al., 1962) have demonstrated that changes in
egg cholesterol occur within hours of treatment. The time course of egg
cholesterol changes thus appears to agree well with the time course
of changes in egg fatty-acid composition (Reiser, l951b).
Data from studies with dietary lipids disclose a large number of un-
certainties. Thus, there is no agreement on whether or not corn oil,
safflower oil, linseed oil, soybean oil, or coconut oil will increase egg
cholesterol. Use of almost every oil at the same level by different
workers has yielded different results. At the present time there is no
good explanation for these serious discrepancies in research results by
reputable, competent scientists.
The inclusion of cholesterol in the diet of the hen promptly causes
increased amounts of cholesterol in the egg. Addition of fat to the diet
along with the cholesterol rather uniformly produces a doubling in egg
cholesterol, probably by increasing the absorption of dietary cholesterol
in the gut.
Agents that influence (a) the intestinal absorption or (b) the
enterohepatic circulation of cholesterol alter egg cholesterol. Thus,
surface-active agents such as Tween or lecithin improve cholesterol
adsorbability and increase egg cholesterol. Conversely, the plant sterol,
,3-sitosterol, promotes the fecal excretion of cholesterol and conse-
quently decreases egg cholesterol. Sitosterol quantitatively replaces
cholesterol in the egg.
Two published reports, which disagree, are inadequate to determine
whether dietary fiber reduces or increases egg cholesterol. The few
studies with vitamins do not demonstrate striking or consistent effects.
D-thyroxine was found to increase egg cholesterol, apparently by stimu
lating cholesterol turnover and excretion via the egg.

210
JOEL BITMAN
Drugs that inhibit the biosynthesis of cholesterol at the reductive
step in the pathway from desmosterol to cholesterol have been successful
in lowering egg cholesterol, but there is an accompanying quantitative
replacement of cholesterol by desmosterol. This alteration raises several
questions:
1. Are eggs containing large quantities of desmosterol satisfactory
as human foods?
2. What level of cholesterol is necessary in the developing ovum to
permit satisfactory egg production?
3. What levels of desmosterol can the chicken successfully cope with?
What are the long-range physiological consequences for the hen of in-
creased levels of desmosterol?
A number of studies have demonstrated that egg cholesterol concen-
tration varies genetically. Eggs from broiler-breeder strains contained
more cholesterol than did those from commercial layer strains (Edwards
et al., 1960; Miller and Denton, 1962; Harris and Wilcox, 1963a; Col-
lins et al., 1968; Turk and Barnett, 1971; Marks and Washburn, 1973;
Cunningham et al., 1974; Washburn and Nix, 1974~. Whether these
differences are large enough to be nutritionally and physiologically
meaningful to humans has not yet been determined.
Many of the substances that have been used in attempts to alter egg
cholesterol are agents that reduce serum cholesterol in other species.
Review of the serum cholesterol changes of the studies summarized in
Table 7 indicated that there was no simple direct relationship between
plasma and egg cholesterol concentration. Thus, both D-thyroxine and
,3-sitosterol lowered blood cholesterol; thyroxine increased egg cho-
lesterol, while sitosterol lowered it. Cholestyramine caused a very large
decrease in serum cholesterol but had no effect upon egg cholesterol.
Feeding dietary oils or oils with cholesterol raised serum cholesterol
and also raised egg cholesterol.
A diagrammatic representation of major cholesterol compartments
of the laying hen is shown in Figure 3. The lack of consistent results
and the lack of understanding of cholesterol relationships in the laying
hen suggest that the time has arrived for complete metabolic balance
studies in egg cholesterol reduction research. Although studies of this
type would be expensive, the many studies listed in Table 7 attest to
the large amount of money already expended on this problem. Measure-
ment of cholesterol levels in the diet, plasma, fat, liver, body, egg, and
excrete; the use of labeled cholesterol; and gas chromatography to
identify egg sterols could bring order to the cholesterol picture order

Alteration of Fatty Acid and Sterol Composition in Lipids 211
,~. LIVER ~
~ ~ ~ ~MACERATE ~ H MG ~ M VA
DIETARY ENTEROHEPATIC / CHOLESTEROL ~ -
1 | CIRCULATION
I N TESTIN A L ~ |
I I ~DIETARY SYNTHETIC
( ~ 1 ~CHOLESTEROL //
~I PLASMA Is - CHOLESTEROL
( ~I CHOLESTEROL I ~ ~
\O
FECES CHOLESTEROL
FIGURE 3 Cholesterol pathways in the laying hen.
-
OVIDUCT =2
CHOLESTEROL
first, of course, and then, it is to be hoped, an elucidation of the laws
governing overall cholesterol metabolism in the chicken. Finally, control
or the possibility of alteration might be feasible if greater understanding
were attained.
A SYNOPSIS OF ALTERATIONS IN THE FATTY ACID
COMPOSITION OF MILK. INFLUENCE OF
UNPROTECTED DIETARY SUPPLEMENTS
Table 8 summarizes data on the alterations in milk fatty-acid composi-
tion that can be effected by unprotected dietary materials. The results of
most studies were in agreement, and the table represents an accounting
of experiments in which minor differences were resolved or ignored
to permit grouping and to develop a typical pattern. Fatty acids not
mentioned in the synopsis are either not altered or not described in the
investigation. Exact details, of course, can only be acquired by con-
sulting the original literature. The effects of season, temperature, fasting,
stage of lactation, and genetics upon the fatty-acid composition of milk
are not described.

214 JOEL BITMAN
The bacteria in the rumen stand as a buffer between the diet and the
metabolic pool that gives rise to milk and meat lipids. Thus, a wide
variety of dietary materials can be ingested; but the bacteria modify
these substances, breaking them down and utilizing them as nutrients
for their own metabolism and growth. This buffering capacity of the
rumen microorganisms thereby produces a rather uniform precursor
pool for lipid synthesis. Consequently, milk retains a fairly constant
composition in the face of great variations in the nature of the diet.
The data of Table 8 illustrate the following facts:
1. Plant oils high in 18:2 increase milk fat 18:2 only slightly; 18:1,
however, increases markedly, indicating that the microorganisms readily
hydrogenate one of the double bonds.
2. The relatively large increase in 18:2 when these same oils are
infused intravenously or intra-abomasally demonstrates that if the
ruminal microorganisms are avoided, and the unsaturated acids enter
the circulation, they are readily transferred into the milk.
3. Feeding pure fatty acids of 12-16 carbon atoms in length did not
provide any evidence of chain elongation, since there were no increases
in Cue acids in milk.
4. Short-chain-length triglycerides, administered intravenously, did
not appear in milk fat to as great an extent as did intermediate and long-
chain triglycerides, suggesting a rapid metabolism of the short-chain
acids. There was evidence of chain elongation of the short-chain
triglycerides.
5. Changing the physical form of the diet (fineness of grind, pellet-
ing, heating) results in an increased transfer of unsaturated lipids into
milk, perhaps because of more rapid passage through the digestive tract
and lessened ruminal hydrogenation.
A SYNOPSIS OF ALTERATIONS IN THE FATTY ACID
COMPOSITION OF MILK. INFLUENCE OF
PROTECTED LIPIDS.
A summary of the alterations that occur in milk fatty acids as a result
of feeding protected lipid-containing materials is presented in Table 9.
The relatively large number of studies attests to the great interest that
this process has stimulated since it was reported 4 years ago (Scott
et al., 19701.
It is clear that protection of the dietary unsaturated lipids enables
them to survive passage through the rumen without undergoing hy-
drogenation and that milk with increased amounts of polyunsaturated
fatty acids can be produced. The levels of linoleic acid in milk fat

216
JOEL BITMAN
equals or exceeds that which can be attained by intravenous or intra-
abomasal infusion. A large number of oils have been encapsulated, and
the results are rather consistent in demonstrating transfer of the main
lipid components of the encapsulated fat into milk.
Search for more economical lipid-feed supplements to replace ex-
pensive, pure vegetable oils, encapsulated with such expensive purified
proteins as casein, has led to the development of a number of seed, bean,
or full-fat flour supplements. In these preparations the native protein
of the plant material is used to encapsulate the lipid, eliminating the use
of casein. The manufacturing technology has also been simplified,
and it has been possible to dry the preparations quickly without the use
of expensive spray-drying equipment.
The efficiency of the transfer of dietary lipids into milk may be a
critical factor in the ultimate success of these protected feed supple-
ments. A difference between 20% and 40% transfer obviously would
make a twofold difference in cost of the supplement. Variability has
been noted in those studies in which efficiency data were supplied
(Table 101. It is not known whether any of the variability in efficiency
of transfer of linoleic acid is associated with the variability in transfer
of fat into milk in different breeds, 3%-4% in Holsteins vs. 6%-8~o
in Jerseys.
A SYNOPSIS OF DAIRY PRODUCTS CONTAINING INCREASED
POLYUNSATURATED FATTY ACIDS
A wide variety of dairy products have been prepared from milk contain-
ing increased amounts of linoleic acid. These products reflect the milk
from which they are made in composition and, generally, are char-
acterized by large increases in 18:2, increases in 18:1 and 18:0, and
decreases in saturated C~-16 fatty acids. A listing of products that
have been made is given in Table 11.
Research on the commercial development of polyunsaturated dairy
products has proceeded intensively in Australia. The altered chemical
and physical properties of the products, oxidative stability, and flavor
are subjects not within the scope of this review and will not be discussed.
A SYNOPSIS OF ALTERATIONS IN FATTY-ACID CONTENT OF
RUMINANT MEAT. INFLUENCE OF UNPROTECTED
DIETARY LIPIDS.
Ruminant depot fats contain very small proportions of polyunsaturated
fatty acids and very small amounts of fatty acids below C14 (Table 2).

218
JOEL BITMAN
TABLE 11 Synopsis of Dairy Products Containing Increased Amounts
of Linoleic Acid
Product
% 18:2 References
Butter
Cheddar cheese
Processed Cheddar cheese
3-33
2-32
Cheedam, Gouda,13rie, 25
Camembert, cream cheeses
Yogurt, sour cream
Margarine
Milk
18-20
5-35
Buchanan et al., 1970; Buchanan and
Rogers, 1973; Harrap, 1973; Kieseker
et al., 1974; Murphy et al., 1974; Wood
et al., 1974; Bitman et al., 1975.
Wang et al., 1973; Czulak et al., 1974a;
Czulak et al., 1974b; Kieseker et al.,
1974; Hodges et al., 1975.
Czulak et al., 1974a; Czulak et al.,
1974b; Hodges et al., 1975.
Herbert and Kearney, 1975.
Johnson et al., 1974; Edmondson et al.,
1974; Johnson, 1974; Johnson and
Tracey, 1974; Sidhu et al., 1974; Stark
and Urbach, 1974.
In contrast to milk, which has about 20%-25~o of C4-C~4 fatty acids,
meat has about 90% of its fatty acids present as palmitic, oleic, and
stearic. The results of the studies summarized in Table 12 make it
abundantly clear that this ruminant adipose tissue composition is re-
markably unresponsive to dietary influences. The rumen and its
microbes modify the dietary components to present a rather constant
precursor pool to the circulation and to the tissues. Also, body depot
fat represents a relatively large compartment that changes only slowly.
The very small differences, of a few percent or no change at all, in
fatty-acid components when large amounts of lipids are fed suggest that
there is very little hope of making significant changes in saturation or
unsaturation of ruminant fats by dietary means. Although changes in
fatty-acid composition induced by breed, age, sex, season, and growth
are not described, these factors also exert influences of about the same
order of magnitude. These studies have been needed, and the develop-
ment of gas chromatography has stimulated an explosion in lipid re-
search because of the relative ease with which fatty acids can be
determined.
It does not appear to be profitable, however, to pursue this type of
meat research further, since there is now adequate proof that ruminant
adipose tissues are essentially insensitive to changes in the fatty-acid
composition of the diet. Slight differences, even those few that are
statistically significant, are only minor perturbations on a background

Alteration of Fatty Acid and Sterol Composition in Lipids 219
of 90% palmitic, oleic, and stearic acids. While of interest scientifically,
they are undoubtedly without physiological or nutritional significance
for the consumer.
A SYNOPSIS OF ALTERATIONS IN THE FATTY-ACID
COMPOSITION OF RUMINANT MEAT. INFLUENCE
OF PROTECTED LIPIDS.
The studies reviewed in Table 13 indicate that feeding protected lipids
will readily increase the polyunsaturation of the depot lipids in cattle
and sheep. When 400-500-lb steers are fed protected lipids they rapidly
take up the dietary linoleic acid such that tissue 18:2 levels approach a
maximum at about 8 weeks. When heavier steers were fed, only small
increases in 18:2 were noted, suggesting a slower turnover and deposi-
tion of lipid in these animals as compared to the more rapidly growing
younger animals.
The protected lipids brought about similar increases in depot fat
18:2 in calves, yielding a polyveal, and in lambs, where the deposition
of dietary 18:2 appears to be particularly rapid. In contrast to the re-
sults with older steers, older sheep responded to dietary 18:2 with a
rapid deposition in depot fat.
The two cheaper seed supplements that have been developed, sun-
flower seed-1 Onto casein-formaldehyde and sunflower seed-soybean
(70:301-formaldehyde, were found to be very effective in producing
polyunsaturated beef, lamb, and mutton.
THE EFFECT OF PROTECTED FEEDS UPON CHOLESTEROL
CONTENT OF MEAT, MILK,AND DAIRY PRODUCTS
We have previously demonstrated that very large increases in plasma
cholesterol occur, from a level of 140 mg % to 380 mg %, when pro-
tected lipids are fed to lactating cows (Bitmap et al., 19731. We had also
earlier reported that there appears to be a rigid blood-milk barrier,
since there was no increase in milk cholesterol in spite of these large
amounts of circulating cholesterol. If the high blood cholesterol
accompanying protected lipid feeding caused deposition of cholesterol
in the tissues, this could negate or counteract possible advantages due
to higher polyunsaturated fatty-acid content. We have examined a
number of food samples in our laboratory and compare these to other
reported values in Table 14. The data show that the cholesterol content
of these polyunsaturated foods was not greater than in conventional
products.

222
JOEL BITMAN
TABLE 13 Effect of Protected Dietary Lipids on Fatty-Acid Compo-
sition of Ruminant Meat a
Diet
14:0 14:1 16:0 16:1 18:0 18:1 18:2 References
Beef
Safflower oil-
casein-F
Sunflower seed-
soybean-F
Veal
Safflower oil-
casein-F
Lamb
Safflower oil-
casein-F
Sunflower seed-
casein-F
Sunflower seed-
soybean-F
Mutton
Safflower oil-
casein-F
Sunflower seed
+ + 42, 56,76,
128, 151
92, 98
+ + 72,116,
228
_ _ + 43
+ 81, 106
- + 98,218
~+ 179
casein-F
81,92
a CODE: + = increase,-= decrease, 0 = no change, and F = fo~,~aldehyde.
S U M MARY
Times change, tastes change, and foods change. The chicken we have
every Sunday is different from those our mothers enjoyed 30 years ago
and different from the chickens our grandmothers ate 60 years ago. The
rapidly growing chicken of today, fed on fish meal and animal tallow,
undoubtedly tastes different from a 1930 bird. The polyunsaturated soft
pork that received much attention 40 years ago may be more acceptable
today, with modern refrigeration and a palate trained by the U.S. food
industry.
In plant research, a firmer tomato is developed with a harder skin
for machine harvesting; sunflowers are developed with higher oil seed
content, and fruits and vegetables are designed to be larger or smaller,
or sweeter or drier, often with great success. Johnson has referred to
this as "biomanipulation," and the introduction of techniques to change
foods of animal origin is a step in the right direction (Johnson 1974~.
I have attempted to outline the past as a step towards filling in the

224
JOEL BITMAN
In Australia, the feed supplement is approved for sale to farmers.
A commercial dairy plant pays a premium to the farmers producing the
milk. A wide range of polyunsaturated foods will soon be sold through
two heart clinics. In New Zealand, four clinics are planning to provide
these new foods for people with greater coronary heart disease risk.
Distribution is being made in this way, because there is not enough food
of this type to meet demand in the open marketplace.
The ability to change foods, and to improve them, is one of the ob-
jectives of the agricultural sciences. These new developments offer
great promise in their ability to bring about lipid changes, but they also
raise new problems. These problems extend over a wide range of science,
from manufacturing technology to the biosynthesis of milk fats. Re-
search directed towards providing foods with altered fat content and
composition is an opportunity to serve the health needs of the nation.
The importance of this type of research rests upon the health problem
that stimulated it. Coronary heart disease is the leading cause of death
in the United States; the best medical and nutritional advice recom-
mends reduction in saturated fats in foods, as well as an overall reduc-
tion in the total amount of fat.
There is not a great likelihood that the preparation of an encapsu-
lated supplement for feeding to a dairy cow to produce polyunsaturated
milk can compete economically with direct homogenization of poly-
unsaturated oils into skim milk. Direct synthetic preparation of poly-
unsaturated cheese and meat is riot presently feasible, however, and the
encapsulation process offers promise, therefore, for preparation of these
foods. While the ultimate commercial future of these products cannot
be assessed, this method provides a possible means whereby traditional
foods can be produced, consumed, and enjoyed by the public without
jeopardy to their health.
R E F E R E N C E S
Agricultural Statistics. 1969. U.S. Department of Agriculture, Washington,
D.C.
2. Amer, M. A., and J. I. Elliot. 1973. Influence of supplemental dietary cop-
per and vitamin E on the oxidative stability of porcine depot fat. I. Anim.
Sci. 37:87.
3. Andrews, J. W., Jr., R. K. Wagstaff, and H. M. Edwards, Jr. 1965. An iso-
topic steady state study of cholesterol in the laying hen. Poult. Sci. 44:
1348.
4. Andrews, J. W., Jr., R. K. Wagstaff, and H. M. Edwards, Jr. 1968. Choles-
terol metabolism in the laying fowl. Am. J. Physiol. 214:1078.
Askew, E. W., J. D. Benson, J. W. Thomas, and R. S. Emery. 1971.
Metabolism of fatty acids by mammary glands of cows fed normal, re

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